The present invention relates to load-compensating mechanism for a gas bearing, in order to maintain a constant bearing gap within a certain load range, wherein the mechanism includes a flexible surface, developed as a metal membrane, on the support side of the gas bearing.
In various fields of use, for example when gas bearings are used for the support of portals of a measuring machine, it is desirable to maintain a constant bearing gap regardless of the load on the bearing, i.e., bearings of very high stiffness are required.
Such a bearing is described in Swiss Patent No. 604033. The known gas bearing contains a resilient support side which is developed as a compliant membrane. This membrane is connected centrally with the base body of the bearing; the edge of the membrane is movably sealed against the inner edge of the bearing housing. The feeding of gas takes place centrally, through the center of the membrane. The membrane and the bearing housing in this way form an inner bearing chamber. In front of this chamber is a choke (bearing nozzle) within the central gas-feed line; and behind the choke, a passage connects the inner bearing chamber with a gas-feed line. The supply pressure P.sub.O is reduced by the choke to the load-dependent pressure P.sub.L. The pressure P.sub.L also prevails in the inner bearing chamber. The stream of gas flows through the central opening in the membrane between the bottom of the membrane and the opposite bearing surface, i.e., the bearing interspace, and emerges at the edge of the bearing. A pressure drop develops along the membrane, from the central gas-feed opening and to the outlet openings.
The cooperative reaction between load pressure P.sub.L in the inner bearing chamber and the pressure drop in the bearing gap is to bend the edge of the membrane in the direction toward the opposite bearing surface. Membrane shape exhibits a convergence in the direction of the stream of gas. Every load increase within a certain load range increases the convergence of the membrane and lifts the bearing, thereby compensating for load-dependent reductions in the bearing gap.
In this way, high rigidity is obtained within a certain operating range.
Stiffness of the described bearing can be increased by providing increased compensation of the bearing. This is obtained by developing a larger membrane surface on the inner-chamber side of the bearing than the active membrane surface on the guide side.
This increased compensation is obtained, however, at a cost disadvantage, in that the membrane of a bearing with increased compensation must be larger than the membrane of a simply compensated bearing; also, the bearing housing must also have a larger circumference than is actually necessary, based on the support surface. And this limitation is not desirable in many cases of use.
Furthermore, the action of this bearing is dependent on the pressure difference between P.sub.O and P.sub.L which develops above the bearing nozzle (choke). However, with high loads, this pressure drop no longer occurs, so that the convergence of the membrane then no longer increases, and the stiffness of the bearing thus decreases.